Abstract
Heavy metals, such as Cr (chromium), have received attention during recent years due to their disposal in soil and water. Brave
peanut (Pterogyne nitens Tul.), a tropical tree, was cultivated in 500 mol L-1 Cr+6 to observe how this species responds to this
stress, with a view to its possible application in the restoration of degraded areas. In the present study, we report the use of a new
method, photoacoustic spectroscopy, to evaluate the emission of CO2 and ethylene and the use of other standard techniques for
assessing stress (chlorophyll a fluorescence, photosynthetic pigment determination, leaf relative water, specific leaf area, NO
(nitric oxide) and polyamines. Photoacoustic spectroscopy appears to provide an innovative and efficient technique for detecting
stress induced by heavy metals soon after their contact with plants. Polyamine content, as well as ethylene and NO, were seen to
be sensitive to Cr+6; polyamines were decreased in leaves and increased in roots, ethylene was increased in the whole plant and
NO was increased in the roots. Our results demonstrating alterations in ethylene in response to Cr+6 are, to date, unreported and
the technique used for these measurements is novel. With regard to the polyamines, modulations in their concentrations may have
protected the photosystem II, since no photosynthetic alterations were observed for pigments and chlorophyll a fluorescence.